Group III nitride compound semiconductor light-emitting element

ABSTRACT

A Group III nitride compound semiconductor light-emitting element (flip chip type light-emitting element) provided with a p-side electrode and an n-side electrode formed on one surface side, wherein the p-side electrode includes: a first metal layer containing Ag and formed on a p-type semiconductor layer; a protective film with which the first metal layer except a part region is covered; and a second metal layer not containing Ag and formed on the protective film.

[0001] The present application is based on Japanese Patent ApplicationsNos. 2001-283994 and 2002-120269, which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a Group III nitride compoundsemiconductor light-emitting element. Particularly, it relates toimprovement of a p-side electrode in a Group III nitride compoundsemiconductor light-emitting element provided with the p-side electrodeand an n-side electrode both formed on one surface side.

[0004] 2. Description of the Related Art

[0005] A so-called flip chip type light-emitting element provided with ap-side electrode and an n-side electrode both formed on one surface sideis known as a Group III nitride compound semiconductor light-emittingelement. The flip chip type light-emitting element is generallyconfigured as shown in FIG. 4. That is, an n-type semiconductor layer102, a light-emitting layer 103 and a p-type semiconductor layer 104 areformed successively on a light-transmissive substrate 101 such as asapphire substrate. A p-side electrode 105 and a protective film 106 areformed on the p-type semiconductor layer 104. An n-side electrode 107 isformed on the n-type semiconductor layer 102. Light emitted from thelight-emitting layer 103 is radiated out through the substrate 101. Onthis occasion, apart of light emitted from the light-emitting layer 103moves toward the electrode side. To improve external radiationefficiency (luminance), it is therefore preferable that the part oflight moving toward the electrode side is efficiently reflected by thep-side electrode 105 so as to be used as external radiating light.Hence, there has been a proposal for a configuration in which Ag (or Agalloy) exhibiting high reflectance to the light emitted from a Group IIInitride compound semiconductor light-emitting element is used as thematerial of the p-side electrode.

[0006] When the p-side electrode is made of such an Ag-based material, ahigh-luminance light-emitting element can be achieved but there arises aproblem in reliability. That is, when the Ag-based material is used,there arises a problem that lowering of intensity of emitted light orreduction of the lifetime is caused by migration of Ag.

[0007] In the related-art example shown in FIG. 4, Ag in the p-sideelectrode 105 is distributed all over the p-side electrode 105 at apoint of time when the protective film 106 is formed by heating afterthe p-side electrode 105 is formed. Further, a window 108 is provided inthe protective film 106 to secure a bonding region. Accordingly, aregion in which Ag is substantially exposed is present, so thatmigration of Ag occurs easily. On the other hand, another configuration(FIG. 5) has been disclosed in Unexamined Japanese Patent PublicationNo. Hei. 11-220171. In the disclosed configuration, a p-side electrode111 made of an Ag-based material is covered with a metal layer 112 notcontaining Ag. A protective film 113 is further formed on the metallayer 112. Hence, the disclosed configuration can be expected toconsiderably suppress migration of Ag from the p-side electrode 111. Aplasma CVD method in a high-temperature state is, however, usedexclusively for forming a protective film 113 good in passivation. Bythis process history, Ag in the p-side electrode 111 is diffused intothe metal layer 112 not containing Ag and provided just above the p-sideelectrode 111. For this reason, similarly to the configuration shown inFIG. 4, migration of Ag cannot be suppressed to a practical levelbecause Ag is diffused into the metal layer surface where the window 114of the protective film 113 is formed although the Ag concentration islow.

SUMMARY OF THE INVENTION

[0008] The invention is designed to solve the problem and an object ofthe invention is to provide a Group III nitride compound semiconductorlight-emitting element with both high luminance and high reliabilityachieved by suppressing migration of Ag in a p-side electrode.

[0009] To achieve the foregoing object, the invention is configured asfollows. That is,

[0010] a Group III nitride compound semiconductor light-emitting elementis provided with a p-side electrode and an n-side electrode both formedon one surface side, wherein the p-side electrode includes: a firstmetal layer containing Ag and formed on a p-type semiconductor layer; anelectrically insulating protective film with which the first metal layerexcept a part region is covered; and a second metal layer not containingAg and formed on the protective film.

[0011] According to this configuration, first, the light-emittingelement can be provided as a light-emitting element high in externalradiation efficiency because the use of the first metal layer containingAg makes the semiconductor layer side surface of the p-side electrodehave high reflectance so that light emitted from the light-emittinglayer can be efficiently reflected by this surface. Moreover, migrationof Ag from the first metal layer to the second metal layer can besuppressed effectively because the first metal layer and the secondmetal layer are electrically insulated from each other by the protectivefilm except a part region. In other words, migration of Ag from thefirst metal layer to the p-side electrode surface (that is, the surfaceof the second metal layer) can be suppressed greatly, so that a highlyreliable light-emitting element can be formed. On the other hand,electrical contact between the first metal layer and the second metallayer can be still sustained by the part region which is not shielded bythe protective film. In this manner, a light-emitting element with bothhigh luminous intensity and high reliability can be provided accordingto the configuration.

[0012] Features and advantages of the invention will be evident from thefollowing detailed description of the preferred embodiments described inconjunction with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In the accompanying drawings:

[0014]FIG. 1 is a schematic sectional view of a light-emitting elementas an embodiment of the invention;

[0015]FIG. 2 is a top view of the light-emitting element;

[0016]FIG. 3 is a partly enlarged view showing the configuration of ap-side electrode in a light-emitting element as another embodiment ofthe invention;

[0017]FIG. 4 is a schematic sectional view showing the configuration ofa related-art light-emitting element;

[0018]FIG. 5 is a schematic sectional view showing the configuration ofanother related-art light-emitting element;

[0019]FIG. 6 is a schematic sectional view of a light-emitting elementas still another embodiment of the invention;

[0020]FIG. 7 is a schematic sectional view of a light-emitting elementas still another embodiment of the invention;

[0021]FIG. 8 is a schematic sectional view of a light-emitting elementas still another embodiment of the invention; and

[0022]FIG. 9 is a plan view of the light-emitting element shown in FIG.8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] A Group III nitride compound semiconductor light-emitting elementaccording to the invention is a so-called flip chip type light-emittingelement provided with a p-side electrode and an n-side electrode bothformed on one surface side. The “flip chip type light-emitting element”means a light-emitting element used in a flip chip type light-emittingdevice, that is, a light-emitting element used after mounted on asupport such as a substrate while the surface side on which the p-sideand n-side electrodes are formed is used as a mount surface. Emittedlight is radiated from the substrate side, that is, a side opposite tothe side where the electrodes are formed.

[0024] The “Group III nitride compound semiconductor light-emittingelement” means a light-emitting element having a light-emitting layermade of Group III nitride compound semiconductor. The Group III nitridecompound semiconductor is represented by the general formulaAl_(X)Ga_(Y)In_(1-X-Y)N (0≦X≦1, 0≦Y≦1, 0≦X+Y≦1), which includesso-called binary compounds such as AlN, GaN and InN, so-called ternarycompounds such as Al_(X)Ga_(1-X)N, Al_(X)In_(1-X)N and Ga_(X)In_(1-X)N(0<x<1), and so-called quarternary compounds such asAl_(X)Ga_(Y)In_(1-X-Y)N (0<x<1, 0<y<1, 0<x+y<1). The Group III elementsmay be partially replaced by boron (B), thallium (Tl), or the like. Thenitrogen (N) may be partially replaced by phosphorus (P), arsenic (As),antimony (Sb), bismuth (Bi), or the like. The Group III nitride compoundsemiconductor layer may contain any optional dopant. Si, Ge, Se, Te, C,or the like, may be used as n-type impurities. Mg, Zn, Be, Ca, Sr, Ba,or the like, may be used as p-type impurities.

[0025] The Group III nitride compound semiconductor layer can be formedby a known method such as a metal organic chemical vapor depositionmethod (MOCVD method), a molecular beam epitaxy method (MBE method), ahalide vapor phase epitaxy method (HVPE method), a sputtering method, anion-plating method, and an electron shower method.

[0026] Incidentally, after doped with p-type impurities, the Group IIInitride compound semiconductor may be subjected to electron beamirradiation, plasma irradiation or heating in a furnace, but this stepis not essential.

[0027] Respective constituent members of the invention will be describedbelow in more detail.

[0028] The p-side electrode includes: a first metal layer containing Agand formed on a p-type semiconductor layer; a protective film with whichthe first metal layer except a part region is covered; and a secondmetal layer not containing Ag and formed on the protective film. Thesecond metal layer contacts the first metal layer at the part region ofthe first metal layer. Hence, the first metal layer, the protective filmand the second metal layer are laminated successively viewed from thep-type semiconductor layer side. Although description in thisspecification is made upon the case where the laminate of the firstmetal layer, the protective film and the second metal layer is referredto as “p-side electrode”, it maybe also conceived that only the firstmetal layer is regarded as a p-side electrode and the protective filmand the second metal layer are regarded as a protective film and a metallayer formed successively on the p-side electrode. Furtheralternatively, it may be conceived that the laminate of the first metallayer and the protective film is regarded as a p-side electrode and thesecond metal layer is regarded as a metal layer formed on the p-sideelectrode.

[0029] The first metal layer is a metal layer containing Ag. When Ag iscontained in the first metal layer, the surface of the first metal layerexhibits high reflectance so that light emitted from the light-emittinglayer can be efficiently reflected by the p-side electrode surface.

[0030] Preferably, Ni, Co, Au, Pd, Pt, etc. may be added to the firstmetal layer in order to improve adhesive property between the firstmetal layer and the p-type semiconductor layer. At least two membersselected from this group optionally may be used in combination.

[0031] Although the first metal layer may be formed as a single layer ofAg or Ag alloy, it is preferable that the first metal layer is formed asa laminate of a plurality of layers different in composition. Forexample, a laminate of a layer for enhancing adhesive property betweenthe first metal layer and the p-type semiconductor layer (hereinafterreferred to as “first adhesive layer”) and a layer of an Ag-basedmaterial (Ag or Ag alloy) (hereinafter referred to as “Ag-based materiallayer”) may be used as the first metal layer. According to thisconfiguration, the first adhesive layer can enhance adhesive propertybetween the p-type semiconductor layer and the Ag-based material layer,so that the first metal layer can be consequently formed on the p-typesemiconductor layer with high adhesive property. Examples of thematerial for forming the first adhesive layer include Ni, Co, Au, Pd,and Pt. At least two members selected from this group may be used incombination. Ag may be used as one of materials for forming the firstadhesive layer.

[0032] The first adhesive layer used here may be constituted by at leasttwo layers different in composition. For example, the first adhesivelayer may be constituted by a lower layer of Ni, Co, Pd or Pt and anupper layer of Au or Au alloy. According to this configuration, adhesiveproperty between the first adhesive layer and the Ag-based materiallayer formed thereon can be improved more greatly, so that the firstmetal layer can be bonded onto the p-type semiconductor layer withhigher reliability. When the first adhesive layer is constituted by twolayers, that is, upper and lower layers, it is preferable that thethickness of the lower layer is smaller than that of the upper layer.This is because increase in contact resistance between the p-typesemiconductor layer and the first metal layer due to the lower layer canbe suppressed when the lower layer is made thin. This is also becausethe lower layer and the Ag-based material layer can be bonded to eachother well by the upper layer when the upper layer is made thick to acertain degree. The thickness of the lower layer is, for example, in arange of from 0.1 nm to 50 nm, preferably in a range of from 0.5 nm to20 nm. The thickness of the upper layer is, for example, in a range offrom 1 nm to 500 nm, preferably in a range of from 5 nm to 200 nm.

[0033] Preferably, a layer for enhancing adhesive property between theAg-based material layer and the protective layer which will be describedlater (hereinafter referred to as “second adhesive layer”) may be formedon the Ag-based material layer. That is, a configuration in which thefirst adhesive layer, the Ag-based material layer and the secondadhesive layer are laminated successively may be provided as a preferredembodiment of the first metal layer. The second adhesive layer may bemade of a material such as Al, Ti, Cr, Ni, Co, Au, Pd or Pt.Alternatively, at least two selected from these materials may be used incombination. Ag may be used as one of materials for forming the secondadhesive layer.

[0034] The second adhesive layer may be constituted by at least twolayers different in composition. For example, the second adhesive layermay be constituted by two layers, that is, a lower layer of Au or Aualloy and an upper layer of Al, Ti, Cr, Ni, Co, Pd or Pt. According tothis configuration, adhesive property between the second adhesive layerand the protective film (which will be described later) formed thereoncan be improved.

[0035] The thickness of each layer in the case where the second adhesivelayer is constituted by two layers, that is, an upper layer and a lowerlayer, is not particularly limited. For example, the thickness of thelower layer is in a range of from 1 nm to 1,000 nm, preferably in arange of from 10 nm to 300 nm. The reason why the thickness range of thelower layer is adopted thus is as follows. If the Au layer orAu-containing layer which is the lower layer is too thick, Ag is mixedwith Au easily so that reflectance of Ag is lowered due to alloying ofAg with Au at the time of heating. If the Au layer or Au-containinglayer which is the lower layer is contrariwise too thin, adhesivestrength between Ag and the upper layer is lowered. For example, thethickness of the upper layer is in a range of from 1 nm to 1,000 nm,preferably in a range of from 10 nm to 300 nm. The reason why thethickness range of the upper layer is adopted thus. is as follows. Ifthe upper layer is too thin, adhesive strength between the upper layerand the protective film or second metal layer formed thereon is lowered.If the upper layer is contrariwise too thick, the amount of a metaldiffused into the Ag layer is increased to thereby cause increase incontact resistance.

[0036] Preferably, the total thickness of the first metal layer is in arange of from 50 to 3,000 nm. If the first metal layer is thinner than50 nm, light reflectance is lowered. If the first metal layer is thickerthan 3,000 nm, the problem in increase of resistance value and increaseof production cost is manifested. Further preferably, the thickness ofthe first metal layer is in a range of from 200 nm to 1,500 nm.

[0037] An electrically insulating protective film is formed on the firstmetal layer. The protective film is formed so that the first metal layerexcept a part region is covered with the protective film. Preferably,the protective film is formed so that the exposed surface of the firstmetal layer, that is, an upper surface and side surfaces of the firstmetal layer can be wholly covered with the protective film and so thatthe protective film has at least one through-hole which reaches theupper surface of the first metal layer. According to this configuration,electrical contact between the first metal layer and the second metallayer (which will be described later) formed on the protective film canbe sustained through the through-hole reaching the upper surface of thefirst metal layer while migration of Ag in the first metal layer issuppressed extremely. Because the path through which Ag in the firstmetal layer can be substantially migrated is only the through-hole, theamount of migration of Ag can be suppressed greatly. Preferably, thethrough-hole is made minute in order to reduce the amount of migrationof Ag more. For example, the diameter of the through-hole is preferablyset to be not larger than 50 μm. The diameter of the through-hole isfurther preferably set to be not larger than 10 μm. The lower limit ofthe diameter of the through-hole is not particularly limited. Forexample, the diameter of the through-hole is set to be in a range offrom 0.1 μm to 50 μm, preferably in a range of from 1 μm to 50 μm,further preferably in a range of from 1 μm to 10 μm.

[0038] A plurality of through-holes may be provided in the protectivefilm. According to this configuration, the Ag migration suppressingeffect obtained by current dispersion can be fulfilled as well as thecurrent path is dispersed to make electrical characteristic good. When aplurality of through-holes are provided, the through-holes arepreferably positioned so that the through-holes are provided to bedispersed as evenly as possible. According to this configuration, thecurrent path in the p-side electrode can be dispersed so evenly thatimprovement of electrical characteristic can be attained. For example, aplurality of through-holes can be provided at regular intervals on theouter circumferential portion of the upper surface of the first metallayer.

[0039] Examples of the electrically insulating material for forming theprotective film include silicon oxide, silicon nitride, aluminum oxide,and titanium nitride. Specific examples thereof which can be usedinclude SiO₂, Si₃O₄, SiN_(x), SiO_(x)N_(y), Al₂O₃, and TiN.

[0040] The thickness of the protective film is not particularly limited.For example, the thickness of the protective film can be set to be in arange of from 50 nm to 500 nm, preferably in a range of from 200 nm to3,000 nm. This is because the side surfaces of the first electrode layercan be covered (subjected to side coverage or step coverage) steadilywhen the protective film is made thicker than the first electrode layer.This is also because production efficiency is lowered if the protectivefilm is too thick.

[0041] The second metal layer is formed on the protective film. Thesecond metal layer is a metal layer which does not contain Ag and whichcan be made of one member selected from the group consisting of Ti, Au,V, Ni, Cr, Zr, Co, Au, Rh, Pt, Cu, Al, Mg, Pd, Mn, Bi, Sn, and Re.Alternatively, the second metal layer may be made of at least twomembers optionally selected from this group.

[0042] The second metal layer may be formed as a laminate of at leasttwo layers different in composition. For example, the second metal layermay be constituted by a laminate of a lower layer of Ti, Au, V, Ni, Cr,Zr, Co, Rh, Pt, Cu, Al, Mg, Pd, Mn, Bi, Sn or Re and an upper layer ofAu or Au alloy. According to this configuration, good adhesive propertybetween the second metal layer and the protective film and good adhesiveproperty between the second metal layer and an Au bump used for junctionwith an external substrate or the like can be obtained. Incidentally,from the point of view of facilitating formation of the second metallayer by vapor deposition and obtaining extremely excellent adhesiveproperty between the second metal layer and the protective film, it isparticularly preferable that Ti, Cr or V is used as the material of thelower layer.

[0043] When the second metal layer is constituted by two layers, thatis, a lower layer and an upper layer, it is preferable that the lowerlayer is thinner than the upper layer. This is because it is conceivablethat, if the lower layer is made thicker, the component of the lowerlayer is diffused into the first electrode layer by long-term currentconduction and thermal load to thereby increase contact resistancebetween the p-type layer and the first electrode layer. This is alsobecause good adhesive property between the second metal layer and an Aubump can be ensured in assembling when the upper layer is made thicker.For example, the thickness of the lower layer is in a range of from 1 nmto 1,000 nm, preferably in a range of from 5 nm to 200 nm. For example,the thickness of the upper layer is in a range of from 50 nm to 10,000nm, preferably in a range of from 200 nm to 2,000 nm.

[0044] The total thickness of the second metal layer is not particularlylimited. For example, the total thickness of the second metal layer ispreferably set to be in a range of from 100 nm to 10 um. When thethickness is set to be not smaller than 100 nm, electrical contactbetween the second metal layer and the first metal layer can be securedsufficiently and adhesive property between the second metal layer and anAu bump in assembling can be secured sufficiently. On the other hand,when the thickness is set to be not larger than 10 μm, increase inresistance value and increase in production cost can be suppressed.

[0045] Further preferably, the thickness of the second metal layer is ina range of from 200 nm to 3,000 nm.

[0046] For example, the light-emitting element according to theinvention can be produced as follows.

[0047] First, a substrate on which Group III nitride compoundsemiconductor layers can be grown is prepared. A plurality ofsemiconductor layers are laminated on the substrate so that an n-typeGroup III nitride compound semiconductor layer, a layer containing alight-emitting layer of a Group III nitride compound semiconductor and ap-type Group III nitride compound semiconductor layer are arranged asthe plurality of semiconductor layers in this order. Examples of thematerial of the substrate include sapphire, spinel, silicon, siliconcarbide, zinc oxide, gallium phosphide, gallium arsenide, magnesiumoxide, manganese oxide, and Group III nitride compound semiconductormonocrystal.

[0048] Then, etching is applied to thereby reveal a part of the n-typesemiconductor layer. Then, both the p-side electrode and then-sideelectrode are formed on the p-type Group III nitride compoundsemiconductor layer and the n-type Group III nitride compoundsemiconductor layer respectively. The p-side electrode can be formed asfollows. First, a first electrode layer is formed by a known method suchas an MBE method, a vacuum vapor deposition method or a sputteringmethod. Then, an electrically insulating protective film is formed by amethod such as a plasma CVD method, a sputtering method or a vacuumvapor deposition method so that a surface of the first metal layer iscovered with the protective film. Then, at least one through-hole isprovided in a part of the protective film by a method such asphoto-etching so that the hole reaches the surface of the first metallayer. Then, a second metal layer is formed on the protective film inthe same manner as the first metal layer.

[0049] The n-side electrode can be formed by a known method such as avacuum vapor deposition method or a sputtering method.

[0050] As described above, the p-side electrode in the invention isconfigured so that a laminate of the first metal layer, the protectivefilm and the second metal layer in this order is formed as the p-sideelectrode after the p-type semiconductor layer is formed. It ispreferable that heating is performed at a temperature not higher thanthe deposition temperature of the Group III nitride compoundsemiconductor before the second metal layer is formed (that is, afterthe first metal layer is formed or after the protective film is formed).By the heating, interfacial resistance between the first metal layer andthe p-type semiconductor layer can be reduced, so that a light-emittingelement excellent in electrical characteristic can be produced. Thetemperature required for the heating here is particularly preferably setto be in a range of from 400° C. to 700° C.

[0051] If heating at a high temperature is performed after the formationof the second metal layer, Ag is diffused from the first electrode layerto the second metal layer by the heating to thereby bring about a fearthat the diffusion of Ag may cause migration of Ag to the surface of thesecond electrode layer. When heating is performed before the formationof the second metal layer, such diffusion of Ag can be, however,prevented. In this case, the path through which Ag can be substantiallymigrated to the second electrode layer surface (that is, the p-sideelectrode surface) is only the hole which is provided in the protectivefilm to secure electrical contact. Accordingly, the amount of migrationof Ag can be suppressed greatly.

[0052] The configuration of the invention will be described below inmore detail in connection with embodiments thereof.

[0053] (Embodiment 1)

[0054]FIG. 1 is a view typically showing the configuration of alight-emitting element 1 as an embodiment of the invention.Specifications of respective layers in the light-emitting element 1 areas follows. Layer Composition p-type layer 15 p-GaN: Mg Layer 14containing including an InGaN layer light-emitting layer n-type layer 13n-GaN: Si Buffer layer 12 AlN Substrate 11 sapphire

[0055] The n-type layer 13 made of GaN doped with Si as n-typeimpurities is formed on the substrate 11 through the buffer layer 12.Although this embodiment has been described upon the case where sapphireis used as the material of the substrate 11, the material of thesubstrate 11 is not limited thereto. For example, sapphire, spinel,silicon, silicon carbide, zinc oxide, gallium phosphide, galliumarsenide, magnesium oxide, manganese oxide, or Group III nitridecompound semiconductor monocrystal may be used as the material of thesubstrate 11. Although this embodiment has been described upon the casewhere the buffer layer is made of AlN by an MOCVD method, the materialand method for forming the buffer layer are not limited thereto. GaN,InN, AlGaN, InGaN, AlInGaN, or the like, may be used as the material ofthe buffer layer. A molecular beam epitaxy method (MBE method), a halidevapor phase epitaxy method (HVPE method), a sputtering method, anion-plating method, an electron shower method, or the like, maybe usedas the method for forming the buffer layer. When Group III nitridecompound semiconductor is used as the material of the substrate, thebuffer layer may be omitted.

[0056] Further, the substrate and the buffer layer can be removed ifnecessary after the semiconductor element is formed.

[0057] Although this embodiment has shown the case where the n-typelayer is made of GaN, the invention may be applied also to the casewhere AlGaN, InGaN or AlInGaN is used as the material of the n-typelayer.

[0058] Although this embodiment has shown the case where the n-typelayer is doped with Si as n-type impurities, the invention may beapplied also to the case where Ge, Se, Te, C, or the like, is used asn-type impurities.

[0059] The n-type layer 13 may be of a double-layered structure with ann⁻ layer of low electron density on the layer 14 side and an n⁺ layer ofhigh electron density on the buffer layer 12 side.

[0060] The layer 14 may contain a light-emitting layer having a quantumwell structure. A single or double hetero type structure or ahomojunction type structure may be used as the structure of thelight-emitting element.

[0061] The layer 14 may contain a Group III nitride compoundsemiconductor layer doped with an acceptor such as magnesium on thep-type layer 15 side and having a wide band gap. This is a technique foreffectively preventing electrons injected into the layer 14 fromdiffusing into the p-type layer 15.

[0062] The p-type layer 15 made of GaN doped with Mg as p-typeimpurities is formed on the layer 14. Alternatively, the p-type layermay be made of AlGaN, InGaN or InAlGaN. Zn, Be, Ca, Sr or Ba may be usedas p-type impurities instead.

[0063] The p-type layer 15 may be of a double-layered structure with ap⁻ layer of low hole density on the layer 14 side and a p⁺ layer of highhole density on the electrode side.

[0064] In the light-emitting diode configured as described above, eachof the Group III nitride compound semiconductor layers may be formed byexecution of MOCVD in a general condition or may be formed by a methodsuch as a molecular beam epitaxy method (MBE method), a halide vaporphase epitaxy method (HVPE method), a sputtering method, an ion-platingmethod or an electron shower method.

[0065] After the p-type layer 15 is formed, the p-type layer 15, thelayer 14 and the n-type layer 13 are partially removed by etching tothereby reveal a part of the n-type layer 13. A V film 20 nm thick andan Al film 2,000 nm thick are formed successively on the revealed partof the n-type layer 13 by vapor deposition. Thus, the n-side electrode50 is formed.

[0066] Sequentially, a first metal layer 20 of Ag is formed on apredetermined region on the p-type layer 15 by vapor deposition so thatthe first metal layer 20 has a thickness of 300 nm. After that, thefirst metal layer 20 is alloyed in the condition of about 600° C. for 3minutes and in an N₂ atmosphere. Then, an SiO₂ film 30 as a protectivefilm with a thickness of 300 nm is formed by a plasma CVD method so thatthe whole surface of the fist metal layer 20 is covered with the SiO₂film 30. Then, through-holes 31 each having a diameter of 50 nm andpassing through the SiO₂ film 30 are provided by etching as shown inFIGS. 1 and 2. Incidentally, FIG. 2 is a top view of the light-emittingelement 1.

[0067] Then, a second metal layer 40 of Au is formed on the SiO₂ film 30so that the second metal layer 40 has a thickness of 1,500 nm. Afterthese steps, the wafer is separated into chips by use of a scriber orthe like.

[0068] (Embodiment 2)

[0069] A light-emitting element 2 as another embodiment of the inventionwill be described below. In the light-emitting element 2, aconfiguration constituted by a plurality of layers is used as theconfiguration of each of the first metal layer formed on the p-typelayer and the second metal layer formed through the protective film.That is, as shown in FIG. 3, a first metal layer 20 a constituted by alaminate of a first layer 21 of Co, a second layer 22 of Au, a thirdlayer 23 of Ag, a fourth layer 24 of Au and a fifth layer 25 of Ni inthis order, and a second metal layer 40 a constituted by a laminate of aTi layer 41 and an Au layer 42 in this order are used. Thelight-emitting element 2 as to the other configuration thereof is thesame as the light-emitting element 1 (see FIGS. 1 and 2). The firstlayer 21 and the second layer 22 serve as the first adhesive layer, andthe fourth layer 24 and the fifth layer 25 serve as the second adhesivelayer.

[0070] The light-emitting element 2 is formed as follows. A first layer21 of Co, a second layer 22 of Au, a third layer 23 of Ag, a fourthlayer 24 of Au and a fifth layer 25 of Ni are formed successively on apredetermined region on the p-type layer 15 by vapor deposition so thatthe layers 21 to 25 have thicknesses of 1 nm, 15 nm, 300 nm, 50 nm and50 nm respectively. Thus, a first metal layer 20 a is formed. Then, thefirst metal layer 20 a is alloyed in the condition of about 600° C., for3 minutes and in an N₂ atmosphere. Then, an SiO₂ film 30 with athickness of 300 nm is formed by a plasma CVD method so that the wholesurface of the first metal layer 20 a is covered with the SiO₂ film 30.Then, through-holes 31 each having a diameter of about 50 nm and passingthrough the SiO₂ film 30 are provided by etching in the same manner asin the light-emitting element 1 (see FIGS. 1 and 2).

[0071] Then, a Ti layer 41 with a thickness of 50 nm and an Au layer 42with a thickness of 1,500 nm are formed successively on the SiO₂ film 30by vapor deposition. Thus, a second metal layer 40 a is formed. Afterthese steps, the wafer is separated into chips by use of a scriber orthe like.

[0072] The reliability of the light-emitting element 2 obtained thus isevaluated in comparison with the related-art configuration (FIG. 4). Thereliability (durability) is evaluated on the basis of Ir which ismeasured after current conduction is performed continuously for 1,000hours in the condition of temperature 85° C., humidity 85% and If(forward)=5 mA. As a result, Ir (reverse) in all of 10 samples of thelight-emitting element 2 is smaller than 1 μA whereas Ir in 4 of 10samples of the related-art light-emitting element (FIG. 4) is notsmaller than 10 μA. It is confirmed that the light-emitting element 2has high reliability because migration of Ag can be prevented. BecauseAg exhibits high reflectance to the emitted light, it is also confirmedthat luminous intensity in the configuration of Embodiment 1(light-emitting element 1) is increased by about 40% and luminousintensity in the configuration of Embodiment 2 (light-emitting element2) is increased by about 30% compared with the related-artconfiguration.

[0073] (Embodiment 3)

[0074] A light-emitting element as a third embodiment of the inventionwill be described with reference to FIG. 6. The same reference numbersare used for the same parts illustrated in FIG. 1, and the explanationof such parts is omitted.

[0075] In a light-emitting element 201 according to the presentembodiment, in addition to the configuration of the light-emittingelement 1 in FIG. 1, the periphery of the second metal layer is expandedto cover the whole upper surface and the side surfaces of the protectivefilm 30. By perfectly covering the protective film 30 with a secondmetal layer 240 as configured in this embodiment, the reflection amountof the emitted light by the second metal layer may be increased toenhance the light emission intensity as well as migration of the firstmetal layer may be securely prevented.

[0076] (Embodiment 4)

[0077] A light-emitting element as a fourth embodiment of the inventionwill be described with reference to FIG. 7. The same reference numbersare used for the same parts illustrated in FIG. 1, and the explanationof such parts is omitted.

[0078] In a light-emitting element 301 according to the presentembodiment, in addition to the configuration of the light-emittingelement 1 in FIG. 1, the protective film is extended to form an extendedpart 331 to there by also cover an etching end face (junction part). Theoccurrence of leak current can be prevented under this configuration. Inorder to more securely prevent the occurrence of the leak current, it ispreferable to cover also apart of the surface of the n-side electrode 50by a protective film 330 as shown in FIG. 7.

[0079] (Embodiment 5)

[0080] A light-emitting element as a fifth embodiment of the inventionwill be described with reference to FIGS. 8 and 9. The same referencenumbers are used for the same parts illustrated in FIG. 1, and theexplanation of such parts is omitted.

[0081] In a light-emitting element 401 according to the presentembodiment, in addition to the configuration of the light-emittingelement 1 in FIG. 1, the protective film is extended to coversubstantially the whole surface of the element except the surface of then-side electrode 50 as illustrated in FIG. 9. The reference number 435designates an opening of a protective film 430. The occurrence of leakcurrent can be prevented by covering the whole surface of the elementwith the protective film 430.

[0082] This invention is not at all limited to the description of themode for carrying out the invention. This invention includes variousmodifications that can be conceived easily by those skilled in the art,without departing from the scope of claim.

[0083] The following items will be disclosed.

[0084] (10) A Group III nitride compound semiconductor light-emittingelement according to the present invention, wherein the thickness of thefirst metal layer is in a range of from 50 nm to 3,000 nm.

[0085] (11) A Group III nitride compound semiconductor light-emittingelement according to the present invention and the item (10), whereinthe thickness of the protective film is in a range of from 50 nm to5,000 nm.

[0086] (12) A Group III nitride compound semiconductor light-emittingelement according to the present invention and the items (10) and (11),wherein the thickness of the second metal layer is in a range of from100 nm to 10 μm.

[0087] (20) A Group III nitride compound semiconductor light-emittingelement according to the present invention and the items (10) through(12), wherein the diameter of the hole is not larger than 50 um.

[0088] (21) A Group III nitride compound semiconductor light-emittingelement according to the present invention and the items (10) through(12), wherein the diameter of the hole is in a range of from 1 μm to 50μm.

[0089] (30) A p-side electrode for a Group III nitride compoundsemiconductor light-emitting element includes: a first metal layercontaining Ag and formed on a p-type semiconductor layer; anelectrically insulating protective film with which the first metal layerexcept a part region is covered; and a second metal layer not containingAg and formed on the protective film.

[0090] (31) A p-side electrode for a Group III nitride compoundsemiconductor light-emitting element according to the item (30),wherein: the protective film is formed so that an upper surface and sidesurfaces of the first metal layer are wholly covered with the protectivefilm; and the protective film has through-holes which reach the uppersurface of the first metal layer.

[0091] (32) A p-side electrode for a Group III nitride compoundsemiconductor light-emitting element according to the item (30) or (31),wherein the first metal layer contains at least one member selected fromthe group consisting of Ni, Co, Au, Pd, and Pt.

[0092] (33) A p-side electrode for a Group III nitride compoundsemiconductor light-emitting element according to any one of the items(30) through (32), wherein the protective film is made of one memberselected from the group consisting of silicon oxide, silicon nitride,aluminum oxide, and titanium nitride.

[0093] (34) A p-side electrode for a Group III nitride compoundsemiconductor light-emitting element according to any one of the items(30) through (33), wherein the second metal layer contains at least onemember selected from the group consisting of Ti, Au, V, Ni, Cr, Zr, Co,Rh, Pt, Cu, Al, Mg, Pd, Mn, Bi, Sn, and Re.

[0094] (35) A p-side electrode for a Group III nitride compoundsemiconductor light-emitting element according to any one of the items(30) through (34), wherein the first metal layer is constituted by aplurality of layers different in composition.

[0095] (36) A p-side electrode for a Group III nitride compoundsemiconductor light-emitting element according to any one of the items(30) through (35), wherein the second metal layer is constituted by aplurality of layers different in composition.

[0096] (50) A method of manufacturing a Group III nitride compoundsemiconductor light-emitting element provided with a p-side electrodeand an n-side electrode both formed on one surface side, the methodincluding:

[0097] a first step of forming a first metal layer containing Ag on ap-type semiconductor layer;

[0098] a second step of forming an electrically insulating protectivefilm with which the first metal layer is covered except a part region;and

[0099] a third step of forming a second metal layer not containing Ag onthe protective film.

[0100] (51) A method of manufacturing a Group III nitride compoundsemiconductor light-emitting element according to the item (50), whereinthe second step includes the steps of: forming an electricallyinsulating protective film with which the first metal layer is covered;and forming at least one through-hole in the protective film so that thethrough-hole reaches a surface of the first metal layer.

[0101] (52) A method of manufacturing a Group III nitride compoundsemiconductor light-emitting element according to the item (50) or (51),further including a step of heating the first metal layer at atemperature not higher than the decomposition temperature of Group IIInitride compound semiconductor, the step being carried out between thefirst step and the second step.

[0102] (53) A method of manufacturing a Group III nitride compoundsemiconductor light-emitting element according to the item (52), whereinthe heating step is carried out at a temperature in a range of from 400°C. to 700° C.

What is claimed is:
 1. A Group III nitride compound semiconductorlight-emitting element having a p-side electrode and an n-side electrodeboth formed on one surface side, wherein said p-side electrodecomprises: a first metal layer containing Ag and formed on a p-typesemiconductor layer; an electrically insulating protective film withwhich said first metal layer is covered except a part region thereof;and a second metal layer not containing Ag, said second metal layerbeing formed on said protective film and contacting said first metallayer at said part region of said first metal layer.
 2. A Group IIInitride compound semiconductor light-emitting element according to claim1, wherein said protective film is formed so that an upper surface andside surfaces of said first metal layer are wholly covered with saidprotective film, and said protective film has a through hole whichreaches said upper surface of said first metal layer.
 3. A Group IIInitride compound semiconductor light-emitting element according to claim1, wherein said first metal layer further contains at least one memberselected from a group consisting of Ni, Co, Au, Pd, and Pt.
 4. A GroupIII nitride compound semiconductor light-emitting element according toclaim 1, wherein said protective film is made of one member selectedfrom a group consisting of silicon oxide, silicon nitride, aluminumoxide, and titanium nitride.
 5. A Group III nitride compoundsemiconductor light-emitting element according to claim 1, wherein saidsecond metal layer contains at least one member selected from a groupconsisting of Ti, Au, V, Ni, Cr, Zr, Co, Rh, Pt, Cu, Al, Mg, Pd, Mn, Bi,Sn, and Re.
 6. A Group III nitride compound semiconductor light-emittingelement according to claim 1, wherein said first metal layer isconstituted by a plurality of layers different in composition.
 7. AGroup III nitride compound semiconductor light-emitting elementaccording to claim 1, wherein said second metal layer is constituted bya plurality of layers different in composition.